1. Field of the Invention
The invention is generally related to the area of optical information recordable medium. More particularly, the present is related to structures for optical medium for carrying or recording digital information and method for making such optical medium.
2. The Background of Related Art
One of the most popular optical storage medium is DVD (Digital Versatile Disc). Technically, DVD is a relatively new generation of optical disc storage technology. It is much larger in data capacity and faster in reading than CD and can hold cinema-like video, better-than-CD audio, still photos, and computer data. DVD aims to encompass home entertainment, computers, and business information with a single digital format. It has replaced laserdisc, is well on the way to replacing videotape and video game cartridges, and could eventually replace audio CD and CD-ROM. DVD has widespread support from all major electronics companies, all major computer hardware companies, and all major movie and music studios. With this unprecedented support, DVD became the most successful storage device of all time in the history of optical storage technologies.
With the popularity of various multimedia applications and data, blank DVD, also called DVDR (i.e., DVD Recordable), is becoming probably the most desirable recordable medium. Users may use DVDR to preserve their own data (e.g., movies, music, and photos). In principle, a DVDR is a blank DVD with a piece of medium that is writable with a laser beam. Data on the same disk can also be read out by the laser beam. Because of the relatively low in cost, DVDR is gaining great popularity among all uses, professional or armature alike.
FIG. 1 shows a cross section view of a structure 100 of a traditional DVDR. As illustrated, there are six layers in a DVDR, a first substrate 10, a dye recording layer 20, a reflective layer 30, an adhesive layer 40, a second substrate 50 and a labeling layer 60. A DVDR is essentially formed by stacking or integrating these six layers on top of each other.
From a user perspective, the labeling layer 60, being a first layer, is for labeling purpose. The labeling layer 60 allows a user to write thereon or is printed to indicate the content therein or the data capacity a disk has. A second layer is the second substrate 50 made of, for example, polycarbonate. The second layer is typically relatively thick and provides the physical strength and support of the disk. The third layer is the adhesive layer 40 that is formed by, for example, UV curable glue. Besides protecting the dye recording layer 20 and the reflective layer 30, the third layer bonds the first substrate 10 and the second substrate 50 together. The fourth layer is the reflective layer 30 to reflect a laser beam. In general, the reflective layer 30 is made out of a reflective material, such as silver with 99.99% purity. The fifth layer is the dye recording layer 20 that records and preserves data. Accordingly, the dye recording layer 20 affects substantially the quality of a disk. The sixth layer is the first substrate 10 supporting the dye recording layer 20 and the reflective layer 30. The first substrate 10 and the second substrate 50 are bonded together to hold both the reflective layer 30 and the dye recording layer 20 therebetween to form a disc (with the labeling layer).
Given the structure 100 of the traditional DVDR, the manufacturing process may be summarized as follows: providing a first substrate, forming a dye recording layer on the substrate, metalizing the dye recording layer in vacuum to form a reflective layer, then applying a type of adhesive to bond with another substrate to form a disk. A printing layer is applied on top of the disk. In other words, there are five essential steps in manufacturing a DVDR disk, there are molding (to create the substrates), dyeing (to create a dye recording layer), metalizing (to form a reflective layer), bonding (to bond all together), and printing (labeling the final disk).
Metalizing is a very important part of the manufacturing process. It laminates a substrate with a layer of reflective material that reflects a laser beam to read data from the disc or write data into the disc. To facilitate the reading by laser, the material used as the reflective material shall have superior reflectivity, otherwise a reflected light beam would be too weak to read off the data on the disk or write data into the disk. It is known that the wavelength of a laser beam for DVDR is 650 nm. At the wavelength, silver has the highest reflectivity, approaching 98.9% while gold has a reflectivity of 95.5%, copper has a reflectivity of 96.6% and aluminum has a reflectivity of 90.5%. Accordingly, silver is more appropriate than others.
In manufacturing DVDR disks, there is a tremendous requirement for the dryness of the dye recording layer. Practically, it is difficult to have the dye recording layer that is completely dry. There may be a certain level of moisture in the dye material. When the dye recording layer is laminated with a reflective material (e.g., silver), the material could react to the moisture in the dye recording layer, causing bubbles, voids and undesirable results. As a result, the quality of a resultant disc is compromised. The disk may be completely inferior or downgraded, thus increasing the manufacturing cost.
On the other end, the moisture in the adhesive (e.g., glue) applied to bond the substrates may also cause chemical erosion to the silver, thus causing bubbles where air trapped in the bubbles can oxidize silver, leading to voids after sometime. When a disc with bubbles is being read at high spinning speed in a disk drive, the layers in the disc intend to split under the centrifugal force of the spinning. As a result, the stability and lifespan of the disk are affected, and a reading device may be ruined.
There thus a need for improved structures of optical medium (e.g., DVD or DVDR) that can overcome the problems commonly seen in the traditional DVDR.